The Passivhaus standard has been developed to provide a practical methodology for designing and building houses which require very little energy for heating, so little in fact that they require no central heating system, even in the coldest parts of Europe. Note that Passivhaus is about energy use only and does not cover other ecological aspects such as healthy building materials or embodied energythe total amount of energy it takes to make a material (or a building). See more on embodied energy in the way that, say CSHCode for Sustainable Homes. A delightful tool for assessing how green a home is. Unfortunately now withdrawn (2015) by this short sighted government. did.

The standard is now widely accepted, not only by self builders but also by local authorities and housing associations. The basis of the standard is about achieving very low energy use in conjunction with a high standard of comfort and air quality. The actual standard is that

the specific heating demand for space heatingthe heating of the rooms as opposed to the heating of the domestic hot water. See Space heating and Domestic hot water and cooling is less than 15 kWhkilowatt hour. This is a unit to measure an amount of energy. If you run your 30 kW gas boiler for 2 hours a day you use 60 kWh per day/m 2 /yr

the total primary energy use for all appliances, domestic hot water and space heating and cooling is less than 120 kWh/m 2 /yr

(the floor area is measured to the inside face of external walls and ignores internal wall[for the purposes of part E of the Approved Documents] - Any wall that does not have a separating function. thicknesses and certain areas which are not considered habitable such as stairs and landings)

This is achieved by a combination of –

very high insulation in walls, ceilings and floors – typically 300mm thick (with very little thermal bridgingthis is a pathway where heat can easily escape (or get in) through some part of the structure. It is usually caused by some element of structure such as a steel lintel or wooden studwork. Also known as a cold bridge. see more on
thermal bridging) with doors and windows having high values of insulation built in. Glazing is typically triple with low Erefers to glazing with low emissivity. A special coating on the glass prevents radiant heat escaping by reflecting it back into the room. coatings and argon filled. See more on Passivhaus window design

low air infiltration – below 0.6 air changes per hour; enough to provide very high air quality without unnecessarily cooling the building.

compact form which ensures a minimum of heat loss through the fabric. see more

The form factor is a measurement of how compact the house is and gives the ratio of the surface area to the volume. A sprawling building with long thin extensions will be more difficult to heat than a compact one because there will be a large surface area which can lose heat compared with the amount of useable space within it. The easiest house to heat will be a cube shape (or if you want to be pedantic, a sphere).

passive solar collection which is incorporated by having most of the glazing to the south and designing windows with high solar heat-gain coefficients.

heat recovery ventilation which is designed so that the minimum of air necessary to maintain high quality ventilation is achieved, (1m³/m² of floor area/hr). An air to air heat exchanger recovers most of the heat from the outgoing air (usually over 80%). Incoming air first goes through the heat exchanger and then an in-line booster heater which lifts the temperature up to room temperature. It is then distributed by ductwork to the various rooms in the house.

The Passivhaus Institute has an excellent web site called Passipedia which explains all the fundamental principles of the standard and the main web site for all UK things Passivhaus is http://www.passivhaus.org.uk/

Once you design to this level of energy efficiency no central heating system is necessary. Any heating which may be required is added to the incoming ventilation air either directly by an electric heater or (thanks to recent developments) via a ground source heat pump which has its heat output into the ventilation air. This combination of energy saving measures has a built in logic to it.

The rate of air change is minimal but sufficient to guarantee a high level of air quality. It is also a sufficiently low rate to ensure that air is never moving at a speed of more than one tenth of a metre per second, the threshold at which air movement becomes noticeable.

vent outlets ensure there is never a direct draught

The standard allows a maximum heat input of 10W/m2 of floor area which is typically provided by a small heating coil or resistance heater situated after the MVHRMechanical Ventilation with Heat Recovery. This is usually a double fan arrangement which extracts stale air from the house and sucks in fresh air at the same time. As the warm stale air is blown out, heat is extracted from it and passed over to the cool incoming air by means of a heat exchanger. With the latest technology, over 90% of the heat can be recovered. (see Passivhaus standard)
heat exchanger. So for instance a 150m2 house would have an extra heat input on top of solar and internal gains) of 1.5kW under the severest conditions.

Quoting from the Passipedia page on Thermal comfort parameters the criterea for comfort are covered by the following conditions which PassivhausSee more on the Passivhaus standard. The PassivHaus Institute has pioneered a standard for low energy buildings. It includes very low energy usage and ways of achieving this. The word is derived from the idea of buildings which are fundamentally low energy and passive solar heated rather than using extra gadgets to heat them. See Passivhaus for the UK branch of the organisation. design includes:

the sultriness limit in relation to the air humidity is not exceeded,

air speeds are within closely defined limits (for speeds under 0.08 m/s, the number of dissatisfied due to draughts is less than 6%)

the difference between radiant temperature and air temperature remains small,

the difference in the radiant temperature in various directions remains small (less than 5 °C, known as the “radiation temperature asymmetry”),

the indoor air temperature stratification is less than 2 °C between the head and ankles of a seated person,

the perceived temperatures in the room change by no more than 0.8 °C at different locations.

Although on-site generation of energy from sources such as photovoltaics is not an integral part of Passivhaus design there is no reason it cannot be incorporated additionally, possibly at a later date (PVPhoto Voltaic. referring to the generation of electricity from sunlight ready). See Passivhaus PlusA somewhat higher standard than Passivhaus standard with a lower limit for renewable primary energy demand and also a requirement to generate renewable energy on site (or if not possible then investment in off-site generation). (see more at Passivhaus Standard) standard below.

Comparison with SAP in the

Building Regulations

Passivhaus does not prescribe what type of energy is used (except the bit about ‘primary’), or whether it is carbon based: only how much energy is used. This contrasts with the UK building regulationsThese are the mass of regulations that cover safety, health, welfare, convenience, energy efficiency etc. in the way buildings are constructed. Not to be confused with Planning consent (which is more to do with whether you can put up the building in the first place). See more on the regulations which have built in factors in the SAPStandard Assessment Procedure - the method used in the building regulations for calculating the energy use of a house. calculation which take into account the amount of carbon emissions.

The standard assessment procedure (SAP) which is the part of the building regulations used to calculate energy efficiency has its counterpart in the Passivhaus Planning Package. There is a bit of a debate going on as to whether it would be better to adopt the Passivhaus approach rather than the SAP approach to energy calculation. A detailed comparison of the two (originally produced by the AECBthe Sustainable Building Association) is available here. It should be borne in mind that the continental approach to ecological building has tended to separate energy calculations from the ecological and health impact of building materials

Design and certification

To achieve this level of low energy consumption there is a combination of computer aided design and a certification procedure, all based on the experience of the thousands of existing Passivhauses which have been built already, mainly across Europe. See the Passivhaus Institute web site

There is a well developed certification procedure for building components such as doors, windows etc. to gain Passivhaus ratings so that these ratings can be fed into the spreadsheet which produces the final energy use values for a house.

Although the standards are very high and very strict there is (in theory) no restriction on the types of materials used or the design of components such as windows and doors, just so long as the final standards are met. While manufacturers are queuing up to get their products approved, there is still a massive lack of components made in the UK and people tend to get them imported.

Cost

Experience in Germany, Sweden and Austria, where most of the development has been done shows that initially the cost of individual Passivhauses is quite high but that as builders become more conversant with the standards and more local manufacturers produce components then the extra price comes down to about 4 to 6 percent above normal building rates.

Passivhaus refurbishment

The Passivhaus standard for refurbishment can be slightly lower than for new buildings because it is acknowledged that certain aspects of an existing building are difficult to change, e.g. the number of windows and their sizes. This is all covered in a modified standard called EnerPHit where for instance the energy limit is ≤ 25 kWh/m²/yr rather than 15.

One of the most thoroughly thought through renovations of an old house is ‘Under the Sun‘ in Birmingham. This has been successfully brought up to Passivhaus standard.

Passivhaus Plus standard

The Classic passivhaus standard is mainly about reducing energy consumption by incorporating very high levels of insulation, excellent control of air infiltration, the use of passive solar collection (mainly through windows) and high quality MVHR. This is mostly achieved with no ‘gadjets’ or particularly high technology. A passivhaus could probably have been built 50 years ago by someone with access to MVHR technology.

the first UK Passivhaus Plus house at Fulford near York

The Passivhaus Plus standard places the upper limit for total energy demand at 45 kWh/(m²a) rather than 60kWh/(m²a). It also requires a minimum of 60 kWh/(m²a) of electricity generation (either directly from the house site (such as PV) or if that is not possible, then investment in remotely generated sustainable electricity. See more detail on the Passivhaus Trust web site.

Passivhaus Premium

This standard requires a maximum of 30 kWh/(m²a) of energy demand along with at least 120 kWh/(m²a) of electricity generation. See more details on Passipedia

Volfgang Feist and some background to the Passivhaus Institute

Volfgang, a physicist, is the originator of the Passivhaus concept along with Bo Adamson, and there is an interview with him by energy consultant Peter Warm on the background and principles involved. It is in 6 parts.

Passivhaus stove flues

There have been a considerable number of fires in Passivhauses with class 1 heating appliances (such as wood stoves). These have been attributed to heavily insulated and sealed roof areas where heat buildup has occurred, possibly due to fluepipe to conduct gas, typically ventilation air or boiler exhaust. see Flue fires. An article in Green Building magazine, summer 2013 describes one such very serious fire, which although the flue was twin-wall and to current building regulations. pretty much burnt the house down. A Dutch company, Metaloterm, manufacture a high grade insulated flue designed to prevent such fires.

“The Passivhaus Bitesize course introduces the key principles of what makes a good low energy, comfortable building, based on the Passivhaus standard. It is delivered in a series of half-day sessions at city centre venues, making it perfect for those with a busy work timetable.”